sorry if this is a repeat of previously provided info. the dershowitz book is already out (dont know about posner's - i havent read posner but if stanley fish recommends him, he cannot be all that clueless). slate magazine has a "dialogue" between the two on the bush v. gore decision:
http://slate.msn.com/dialogues/01-07-02/dialogues.asp?iMsg=0
the more dialogues link will also yield a discussion between singer and posner on animal rights.
--ravi